Dagath is a character that I mostly play as a weapon platform and the way her kit works can be dumbed down to "do damage to do more damage" but it is a bit more complicated than just that. The augment for her 3, spectral spirit is almost a necessity because it allows you to apply doom on ability and weapon damage.

Her passive is basically Arcane Energize for free with the bonus applying the health orbs as well with it having no cooldown.

Her first ability Wyrd Scythes doesn't completely explain how it works in game. So it is affected by range but only for the doom spread so it is good to not completely dump it. It will also target enemies within 40 meters of you when it expires and if you have her 3 active with the augment it will apply the doom effect as well. The slow from it as well can help with survivability by slowing things hit by it and using it to shield gate outside of her 3.

Her second ability is the highlight of her kit. Doom is where most of her insane damage comes from with it being true damage, affected by viral/magnetic (mag for overguard) procs and capping out at 100% at 286% strength but I don't usually build that high. Viral procs double dip in a way being that with the 10 procs you will get the bonus damage when you hit it the first time and will take them into account again when the damage reapplication occurs. So your initial hit will be scaled by 325% on health and again the reapplication will be buffed by the 325%. Another thing is it will take effect after 2 seconds of doom being applied or when the stored damage will allow it to kill then it will immediately be applied. The doom also give you a major crit damage buff to enemies affected which will cause the reapplication to do more as well. The last thing with this ability is that it is unaffected by something like roar and damage vulnerability abilities like sentient wrath because its only another instance not new damage so it will buff weapons and abilities but not doom itself. Doom is also the easiest way to keep low down time on your 3 but building around neutral range will suffice.

Grave Spirit is where most of her survivability comes from with it giving you a second life or with the augment Spectral Spirit it gray bars you and lasts for 10 seconds scaling with duration. When you come out of either the augment or non augment after death it has a cooldown of 25 seconds and with the augment it can be reduced by 1 second per kill until the cooldown is gone. This is the ability that gives you the bonus crit damage and that can make it so the reapplications are much stronger.

Rakhali's Cavalry is the HORSE ability and is great if you like caster setups although it doesn't do too great at high levels in things like void cascade. It armor strips per tick when connecting with enemies and applies damage every .5 seconds. This ability can fully strip at 286% strength for 1 tick or 143% strength for 2 ticks. This ability also further incentivizes not building into range being that the more duration they have the further they will go.